I am not so sure about the whole union thing. Is it two separate governing bodies for stage actors then film?? And it is probably my own ignorance rearing its ugly head but I always thought it was the agents' abilities or lack there of, to get them more work in the US.
British actors such as, Alan Rickman, Ian McCellan, Patrick Stewart, Heath Ledger, Christian Bales, Kenneth Bragnaugh, Sean Bean, Ewan McGregor, and lets not forget Mel Gibson and Russell Crowe (ok, ok, they are both Austrailians but ...) have been in tons of very sucessful films and most of them household names here in the US, I think (or it could be that I am a bit of a movie nerd)
So I have to wonder if it is really a union thing in particular to the theater or is it agents' lack of abilities to make the necessary contacts in the US?!
OK sorry, I couldn't relate it to dance at all.